Method and system for performing PAL luma two line vertical combing

ABSTRACT

A method and system for performing combing for PAL luma data is disclosed. The combing is performed for a display having a plurality of lines. The display is capable of depicting a frame including a horizontal boundary having a top edge and a bottom edge. A top line of the plurality of lines is at the top edge of the horizontal boundary. A bottom line of the plurality of lines is at the bottom edge of the horizontal boundary. The method and system includes providing a feedback multiplexer, a line delay and a feed forward multiplexer. The feedback multiplexer has a first input, a second input and a first output. The first input is for receiving luma data for a current line. The line delay has a delay input and a delay output, the delay input coupled with the first output. The delay output is coupled with the second input. The feed forward multiplexer has a third input, a fourth input and a second output. The third input is coupled with the delay output. The fourth input is for receiving the luma data for the current line. The feedback multiplexer is controlled to provide fedback luma data from the second input to the first output when the current line is the top line and to provide the luma data for the current line from the first input to the first output otherwise. The feed forward multiplexer is controlled to provide next line luma data from the fourth input to the second output when the current line is the bottom line and to provide the luma data from the current line to the second output otherwise.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is claiming under 35 USC 119(e) the benefit ofprovisional patent Application serial No. to be assigned filed on Nov.6, 2001.

FIELD OF THE INVENTION

[0002] The present invention relates to graphics systems, and moreparticularly to a method and system for performing PAL luma two linevertical combing.

BACKGROUND OF THE INVENTION

[0003] In graphics systems, data for a particular frame includes bothluma (luminance) and chroma (chrominance) data. In order to process thegraphics data, the luma and chroma are separated. The mechanism used toseparate the luma and chroma data depends upon the standard with whichthe data complies. One such standard is PAL. In PAL, luma and chromadata are carried predominantly at two different frequencies. In PAL,frequencies below 3.1 MHz are assumed to be luma. Thus, one conventionalmethod for separating the luma and chroma data uses a band pass filterto remove the low frequency luma data from the chroma data. However,there is some crosstalk between the luma and chroma data. Consequently,some luma data will exist above 3.1 MHz and some chroma data residesbelow 3.1 MHz. In order to better separate the luma and chroma data,another process is used.

[0004]FIG. 1 depicts a high-level block diagram of a conventional system10 for separating PAL luma and chroma data. Typically, luma and chromadata are carried predominantly at two different frequencies. Theconventional system 10 includes a first line delay 16 and a second linedelay 18, adder 20, a divide-by-two block 22 and a subtractor 24. Eachline delay 16 and 18 provides a delay equal to one line being processed.

[0005]FIG. 2 depicts a conventional method 50 for separating PAL lumaand chroma data utilizing conventional three-line combing. Theconventional method 50 is generally used by the system 10. Consequently,the conventional method 50 is described in conjunction with the system10. Referring to FIGS. 1 and 2, the method 50 and the system 10 assumethat the data does not change radically from line to line. Thus, themethod 50 and the system 10 approximate data for the current line usinga previous line and a next line. A portion of the video signal isseparated at the node 11, via step 51. Thus, a portion of the videosignal is transmitted along the line 12, while another portion istransmitted along the line 14. The data is sent through two line delays16 and 18, via step 52. The output of the second delay 18 is data forthe previous line. The data at the node 17 between the line delays 16and 18 is data for the current line. Data taken from the node 11 is datafor the next line. The data for the previous, current and next lines arethus present in the system 10 because of the line delays 16 and 18.

[0006] The previous line and next line signals are combined, via step53. Step 53 is performed by combining the signal from the line 12 withthe signal being output by the second line delay 18 using the combiner20. Because the signal from the second line delay 18 is two lines aheadof the signal taken from the node 11, chrominance data is approximatelycanceled out when the two signals are combined. The output of thecombiner 20 is two times the luma data for the current line. Note thatalthough the output of the combiner 20 is termed twice the luma data forthe current line, the output actually approximates the twice luma datafor the current line because the previous and next lines were used.

[0007] This data is then cut in half, using the divide-by-two block 22,via step 54. Thus, the output of the divide-by-two block 22 is the lumadata for the current line. The luma data output by the divide-by-twoblock 22 is considered to be for the current line because data for thecurrent line is taken from the node 17, between the line delays 16 and18.

[0008] The luma data is then subtracted from the chroma data for thecurrent line; via step 55. This step is performed using the subtractor24. Consequently, the luma data and the chroma data can be output by theconventional system 10.

[0009] Although the conventional system 10 and method 50 functionadequately in most cases, one of ordinary skill in the art will readilyrecognize that the conventional system 10 and method 50 do not work wellat certain rough edges. FIG. 3 depicts a portion of a frame 60 in adisplay. The frame 60 includes such a boundary 90. The boundary 90 isbetween polygons 70 and 80. However, the boundary 90 could be betweenother items. The edge 90 is rough because the polygons 70 and 80 havevery different colors. For example, the polygon 70 may be dark, whilethe polygon 80 may be light. The portion of the polygon 70 shownincludes lines 61, 62 and 63. The portion of the polygon 80 shownincludes lines 64, 65 and 66. The edge 90 is between lines 63 and 64.

[0010] Referring to FIGS. 1-3, the conventional system 10 and method 50combine data for a previous line and a next line in order to obtain lumadata, which is also used to obtain the chroma data. When line 62 is thecurrent line, taken from node 17, line 61 is the previous line and line63 is the next line. Consequently, the luma and chroma data output fromthe divide-by-two block 22 and the subtractor 24 are as desired.However, when line 63 is the current line taken from the node 17, line62 is the previous line and line 64 is the next line. However, line 64is part of the other polygon 80, taken from the other side of the edge90. Consequently, when the line 64 is combined with the line 62, theresultant will not be close to the luma data for the current line. Thisis because the chroma data changes radically due to the boundary 90. Inother words, the assumptions made for performing the conventionalthree-line combing of the method 50 no longer hold. As a result, theappearance of the frame near the boundary 90 is incorrect.

[0011] Accordingly, what is needed is a system and method for separatingPAL luma and chroma data while reducing the incongruities introducedaround rough boundaries. The present invention addresses such a need.

SUMMARY OF THE INVENTION

[0012] The present invention provides a method and system for performingcombing for PAL luma data. The combing is performed for a display havinga plurality of lines. The display is capable of depicting a frameincluding a horizontal boundary having a top edge and a bottom edge. Atop line of the plurality of lines is at the top edge of the horizontalboundary. A bottom line of the plurality of lines is at the bottom edgeof the horizontal boundary. The method and system comprise providing afeedback multiplexer, a line delay and a feed forward multiplexer. Thefeedback multiplexer has a first input, a second input and a firstoutput. The first input is for receiving luma data for a current line.The line delay has a delay input and a delay output, the delay inputcoupled with the first output. The delay output is coupled with thesecond input. The feed forward multiplexer has a third input, a fourthinput and a second output. The third input is coupled with the delayoutput. The fourth input is for receiving the luma data for the currentline. The feedback multiplexer is controlled to provide fedback lumadata from the second input to the first output when the current line isthe top line and to provide the luma data for the current line from thefirst input to the first output otherwise. The feed forward multiplexeris controlled to provide next line luma data from the fourth input tothe second output when the current line is the bottom line and toprovide the luma data from the current line to the second outputotherwise.

[0013] According to the system and method disclosed herein, the presentinvention provides a method and system for performing two-line combingthat reduces artifacts of separation of PAL luma and chroma data.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a high-level block diagram of a conventional system forseparating PAL luma data from PAL chroma data.

[0015]FIG. 2 is a high-level flow chart block diagram of conventionalmethod for separating PAL luma data from PAL chroma data.

[0016]FIG. 3 is a diagram of a portion of a frame in a display.

[0017]FIG. 4 is a block diagram of one embodiment of a system inaccordance with the present invention for performing two line combingfor PAL luma data.

[0018]FIG. 5 is a high-level flow chart of one embodiment of a method inaccordance with the present invention for performing two line combingfor PAL luma data.

[0019]FIG. 6 is a flow chart of one embodiment of a method in accordancewith the present invention for performing two line combing for PAL lumadata.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention relates to an improvement in graphicssystems. The following description is presented to enable one ofordinary skill in the art to make and use the invention and is providedin the context of a patent application and its requirements. Variousmodifications to the preferred embodiment will be readily apparent tothose skilled in the art and the generic principles herein may beapplied to other embodiments. Thus, the present invention is notintended to be limited to the embodiment shown, but is to be accordedthe widest scope consistent with the principles and features describedherein.

[0021] The present invention provides a method and system for performingcombing for PAL luma data. The combing is performed for a display havinga plurality of lines. The display is capable of depicting a frameincluding a horizontal boundary having a top edge and a bottom edge. Atop line of the plurality of lines is at the top edge of the horizontalboundary. A bottom line of the plurality of lines is at the bottom edgeof the horizontal boundary. The method and system comprise providing afeedback multiplexer, a line delay and a feed forward multiplexer. Thefeedback multiplexer has a first input, a second input and a firstoutput. The first input is for receiving luma data for a current line.The line delay has a delay input and a delay output, the delay inputcoupled with the first output. The delay output is coupled with thesecond input. The feed forward multiplexer has a third input, a fourthinput and a second output. The third input is coupled with the delayoutput. The fourth input is for receiving the luma data for the currentline. The feedback multiplexer is controlled to provide fedback lumadata from the second input to the first output when the current line isthe top line and to provide the luma data for the current line from thefirst input to the first output otherwise. The feed forward multiplexeris controlled to provide next line luma data from the fourth input tothe second output when the current line is the bottom line and toprovide the luma data from the current line to the second outputotherwise.

[0022] The present invention will be described in terms of a systemhaving certain components and a method having certain steps. However,one of ordinary skill in the art will readily recognize that the presentinvention will operate effectively for other systems having other and/ordifferent components and methods having additional and/or differentsteps.

[0023] To more particularly illustrate the method and system inaccordance with the present invention, refer now to FIG. 4, depictingone embodiment of a system 100 in accordance with the present inventionfor performing two line combing for PAL luma data. The system 100includes feedback multiplexer 110, line delay 120 and feed forwardmultiplexer 130. The system 100 also may include controller 240 forsetting a control bit. The feedback multiplexer 110 includes inputs 112and 114 and output 116. The line delay 120 delays the signal by a singleline of the frame and includes input 122 and output 124. The feedforward multiplexer 130 includes two inputs 132 and 134 and an output136. The inputs 114 and 132 of the feedback multiplexer 110 and feedforward multiplexer 130, respectively, are coupled to the input 102 ofthe system 100. The input 112 of the feedback multiplexer and the input114 of the feed forward multiplexer are coupled to the output of theline delay 120. The output of the feedback multiplexer 116 is coupled tothe input of the line delay 120. The controller 140 is coupled to theinput 114 of the feedback multiplexer 110. The controller 140 sets acontrol bit based upon an appropriate type of combing provided to theinput 104 of the system 100.

[0024]FIG. 5 is one embodiment of a high-level flow chart of a method200 in accordance with the present invention for performing two linecombing for PAL luma data. The method 200 is preferably performed by thesystem 100. Consequently, the method 100 is described in connection withthe system 100 depicted in FIG. 4. Referring to FIGS. 4 and 5, luma datafor a previous line is used in lieu of luma data for a current line ifthe current line is a top line, via step 202. A top line is the lineabove and adjacent to a boundary. For example, in FIG. 3, the top lineis line 63. Referring to FIGS. 3, 4, and 5, step 202 would use luma datafor line 62 in lieu of line 63. Step 202 is preferably performed usingthe feedback multiplexer 110. When the line being input to the input 114of the feedback multiplexer 110 is a top line, the feedback multiplexer110 selects the other, fedback data from the input 112. This data haspassed through the line delay 224 and is thus from a previous line.This, fedback data is forwarded through the system 100 in lieu of thedata received by the input 114 of the multiplexer 110.

[0025] For a bottom line, luma data from the next line is used insteadof luma data for a bottom line, via step 204. A bottom line is below andadjacent to a boundary such as the boundary 90. Step 204 is preferablyperformed using the feed forward multiplexer 130. When the data for theline provided to the input 134 of the feed forward multiplexer 130 isfor a bottom line, the feed forward multiplexer 130 selects the databeing input via the input 136 for forwarding to the output 136. Thisdata has not passed through the line delay 120 and is thus from the nextline. In other cases, system 100 forwards the data for the current line,via step 206.

[0026]FIG. 6 is a more detailed flow chart of one embodiment of a method210 in accordance with the present invention for performing two linecombing for PAL luma data using the system 100. The method 210 isdescribed in conjunction with the system 100. Referring to FIGS. 4 and6, the system 100 receives the input data through input 202 and anindication of the appropriate type of combing through input 204, viastep 212. The appropriate type of combing may be conventional three linecombing, top two line combing, bottom two line combing or no combing.Top two line combing is used for the top line. Bottom two line combingis appropriate for the bottom line, as defined above. Conventional threeline combing may be used in other cases. The data input through theinput 202 is either combed data or horizontal luma data. The combed datahas preferably undergone conventional three line combing.

[0027] A control bit is then either set or not set, depending upon theappropriate type of combing provided to input 204, via step 214. Step214 is preferably performed by the controller 140, but could beperformed in another manner by another component; The control bit is forthe feed forward multiplexer 130. The control bit is set if no combingis appropriate for the system 100 or if bottom two line combing isappropriate. The control bit and luma data (combed luma data or simplyhorizontal luma data) are provided to the input 114 of the feedbackmultiplexer 100, via step 216.

[0028] It is then determined whether the luma data that is provided tothe feedback multiplexer 110 through input 114 is from a top line, viastep 218. Based on this determination, the control signal 118 controlsthe feedback multiplexer 110. If the data from the input 114 is for atop line (above a boundary), then data that is discarded. Instead, thedata provided to the input 112, which was fed back from the output ofthe line delay 120, is provided to the output 116 from the feedbackmultiplexer 110, via step 220. Otherwise, the data provided to the input114 is provided to the output 116, via step 222. Thus, if the dataprovided to the input 202 of the system 100 and thus to the input 114 ofthe feedback multiplexer 110 is not from a top line, the data will beforwarded by the feedback multiplexer 110. If, however, the dataprovided to the input 202 of the system 100 and thus to the input 114 ofthe feedback multiplexer 110 is from a top line, then data from theprevious line will be used instead. Data from the previous line is thedata fed back from the output 124 of the line delay 120 to the input 112of the feedback multiplexer 110.

[0029] The data output by the feedback multiplexer 110, which includesboth luma data and the control bit, undergoes a one line delay, via step224. Step 224 is performed by sending the data output by the feedbackmultiplexer 110 to the line delay 120. The delayed data including boththe control bit and the luma data is fed back to the feedbackmultiplexer 110 and the control bit is stripped off and the remainingluma data provided to the feed forward multiplexer 130, via step 226. Itis determined whether the luma data provided to the feed forwardmultiplexer 130 from the line delay 120 via the input 134 is a bottomline, via step 228. If the luma data input from the line delay 120 isnot for a bottom line, then the data is output, via step 230. If theluma data input from the line delay 120 is for the bottom line, thendata for the next line is fed forward, via step 232. Step 232 isperformed by selecting the data provided to the input 132 from thesystem input 202 when the luma data is for a top line. In a preferredembodiment, steps 130 and 132 are performed by forwarding data for thenext line when the control bit is set and the appropriate type ofcombing for the next line is three line combing and outputting data fromthe line delay 120 otherwise.

[0030] Thus, the system 100 and methods 200 and 210 perform two linecombing for appropriate portions of a frame. For example, referring backto FIG. 3, the system 100 and methods 200 and 210 perform two linecombing for the lines 63 and 64. In particular, the system 100 andmethods 200 and 210 will simply pass through data for line 62 becausethree line combing is appropriate for line 62. However, line 63 is a topline, a line above and adjacent to a boundary 90. Consequently, thesystem 100 and methods 200 and 210 perform two line combing for the line63. In particular, the system 100 and methods 200 and 210 discard thedata for line 63, and utilize data from line 62 instead. Similarly, line64 is a bottom line, a line below and adjacent to the boundary 90.Consequently, the system 100 and methods 200 and 210 perform two linecombing for the line 64. In particular, the system 100 and methods 200and 210 discard data for the line 64 and utilize data from the line 65.For the line 65, the system 100 and methods 200 and 210 simply pass theluma data through. As a result, the system 100 and methods 200 and 210allow the luma data which may have undergone three line combing and thatare not adjacent to a boundary, such as the boundary 90, to passthrough. However, the system 100 and methods 200 and 210 perform theappropriate type of two line combing for lines that are adjacent toboundaries.

[0031] Because the system 100 and methods 200 and 210 perform two linecombing for top and bottom lines, the luma data at one side of aboundary is not corrupted by luma data from the other side of theboundary that would otherwise be introduced by three line combing. As aresult, artifacts introduced by cross contamination from data on theopposite side of the boundary can be reduced or eliminated.Consequently, the quality of the frame displayed is improved.

[0032] A method and system has been disclosed for performing two-linecombing for PAL luma data. Software written according to the presentinvention is to be stored in some form of computer-readable medium, suchas memory, CD-ROM or transmitted over a network, and executed by aprocessor. Consequently, a computer-readable medium is intended toinclude a computer readable signal which, for example, may betransmitted over a network. Although the present invention has beendescribed in accordance with the embodiments shown, one of ordinaryskill in the art will readily recognize that there could be variationsto the embodiments and those variations would be within the spirit andscope of the present invention. Accordingly, many modifications may bemade by one of ordinary skill in the art without departing from thespirit and scope of the appended claims.

What is claimed is:
 1. A method for performing combing for PAL luma datafor a display having a plurality of lines, the display capable ofdepicting a frame including a horizontal boundary having a top edge anda bottom edge, a top line of the plurality of lines at the top edge ofthe horizontal boundary, a bottom line of the plurality of lines at thebottom edge of the horizontal boundary, the method comprising the stepsof: (a) for the top line, replacing bottom line luma data with previousline luma data; (b) for the bottom line, replacing top line luma datawith subsequent line luma data and (c) for a remaining portion of theplurality of lines, providing three-line combing luma data.
 2. A systemfor performing combing for PAL luma data for a display having aplurality of lines, the display capable of depicting a frame including ahorizontal boundary having a top edge and a bottom edge, a top line ofthe plurality of lines at the top edge of the horizontal boundary, abottom line of the plurality of lines at the bottom edge of thehorizontal boundary, the system comprising: a feedback multiplexerhaving a first input, a second input and a first output, the first inputreceiving luma data for a current line; a line delay having a delayinput and a delay output, the delay input coupled with the first output,the delay output coupled with the second input; a feed forwardmultiplexer having a third input, a fourth input and a second output,the third input coupled with the delay output, the fourth inputreceiving the luma data for the current line, the feedback multiplexerbeing controlled to provide fedback luma data from the second input tothe first output when the current line is the top line and to providethe luma data for the current line from the first input to the firstoutput otherwise, the feed forward multiplexer being controlled toprovide next line luma data from the fourth input to the second outputwhen the current line is the bottom line and to provide the luma datafrom the current line to the second output otherwise.
 3. The system ofclaim 2 further comprising: a first system input, coupled with the firstinput of the feedback multiplexer and the fourth input of the feedforward multiplexer, for receiving the luma data; and a second systeminput, coupled with the first input of the feedback multiplexer, for isreceiving an appropriate combing type, the appropriate combing typebeing three a line combing, a bottom two line combing for the bottomline,.or a top two line combing for the top line.
 4. The system of claim3 further comprising: a controller coupled to the second system inputand the first input of the feedback multiplexer, the controller forsetting or not setting a control bit, the control bit being provided tothe first input of the feedback multiplexer, the control bit being setwhen the current line is the top line or when combing is not performed.5. The system of claim 4 wherein the feed forward multiplexer providesthe next line luma data from the fourth input to the second output whenthe control bit is set and a next line utilizes the three line combing.